Prior research has demonstrated that written exposure therapy (WET), is an efficient, well- tolerated, and efficacious treatment for PTSD. The proposed project takes the next step in establishing WET as an intervention for PTSD by examining whether WET is noninferior to an evidence-based treatment for PTSD. Using a randomized noninferiority controlled trial, 126 adults with a primary diagnosis of PTSD will be assigned to either WET or Cognitive Processing Therapy (CPT). Outcome data will be collected at baseline and 6-, 12-, 18-, 24 and 60-weeks post-baseline. The primary aim is to examine whether PTSD participants assigned to WET demonstrate PTSD symptom severity outcome that is noninferior to PTSD participants assigned to CPT. Secondary aims include examining whether expected treatment gains are sustained for both treatments and whether WET has a lower treatment dropout rate relative to CPT. Exploratory aims include examining moderators and mediators of WET and CPT. If the hypothesis that WET is noninferior to CPT is confirmed then a brief treatment option for PTSD will be established.